1. Field of the Invention
The present invention relates to an apparatus and a method for reducing power consumption of a LCD (Liquid Crystal Display) backlight lamp, and in particular to an apparatus and a method for reducing power consumption of a LCD (Liquid Crystal Display) backlight lamp which is capable of reducing unnecessary power consumption by supplying power from an inverter to a LCD backlight lamp so as to be similar to luminescent characteristics of a LCD backlight lamp.
2. Description of the Prior Art
Generally, a LCD (Liquid Crystal Display) is made up of elements known as pixels for displaying a figure or an image, by injecting liquid crystals between two glass plates, applying power to electrodes installed at the two glass plates and thereby varying the molecular arrangement of the liquid crystals at each pixel location.
However, a LCD (Liquid Crystal Display) panel does not radiate light in itself but transmits light from a backlight installed at a back surface of the panel as a light source, and the backlight lamp is installed in order to display contents more accurately and vividly. In order to operate the backlight lamp, a certain power input condition has to be satisfied, for example, in a monitor having a LCD display apparatus of not greater than 14.1″, an AC voltage of 500˜700V (40˜70 Khz) and current of 1˜7 mA have to be supplied to the backlight lamp.
The backlight lamp is operated by an inverter, and in order to satisfy the above-mentioned input condition, the operation of the inverter has to be controlled. In more detail, the luminescence of the backlight lamp is adjusted by varying the backlight lamp current outputted from the inverter, so that the brightness degree of the backlight lamp becomes greater in proportion to the size of the current supplied to the backlight lamp.
A method for operating the backlight lamp in accordance with the prior art will be described as below.
In order to vary the brightness of a backlight lamp, a brightness variation key is provided in a keyboard of a notebook computer, and a microprocessor reads set variation key value information, transmits a brightness adjustment information signal converted into information required for the brightness adjustment to an inverter, and the inverter controls the brightness of the backlight lamp by generating a backlight lamp current in accordance with the brightness adjustment information signal.
For example, by using a voltage level range of 0˜5V, the microprocessor sets the brightness adjustment information signal for a minimum brightness at a value of 0V and sets the brightness adjustment information signal for a maximum brightness at a value of 5V. In addition, a variable quantity between discrete brightness levels is set as 0.5V. Herein, when the value for the first level is 0V, a minimum brightness value is 0V in a first level, and according to the increase by each level increment the backlight lamp becomes brighter, so that when an eleventh level is 5V, the maximum brightness value is 5V in the eleventh level. Herein, when the operation (driving) current of the backlight lamp is variable between 2˜6 mA and the inverter is designed so as to be variable by levels of 0.5 mA, the first level value is 0V (corresponding to 2 mA), the second level value is 0.5V (corresponding to 2.5 mA), the eleventh level is 5V (corresponding to 6 mA).
In addition, when a user sets the backlight lamp for the maximum brightness, power is off or the backlight lamp is turned off by entering into a suspend mode by a display setting, the microprocessor stores the brightness adjustment information at the time in a memory. Afterwards, when the user turns on the backlight lamp again, the microprocessor reads again the brightness adjustment information stored in the memory or reads brightness adjustment information (example: 8 level) set as a default setting and transmits a brightness adjustment information signal to the inverter, and the inverter controls the brightness of the backlight lamp by generating a backlight lamp current corresponding to the brightness adjustment information signal.
The operation will be described in more detail. As depicted in FIG. 1, when a user sets the backlight lamp as a tenth level (4.5V) brightness in a total of eleven levels, the user turns off the backlight lamp and turns on again the backlight lamp as shown at steps S1, S2, and the microprocessor reads a brightness adjustment information signal (4.5V) stored in a memory and outputs it to the inverter as shown at step S3.
Herein, the inverter outputs a backlight lamp current (5.5 mA) corresponding to the tenth level (4.5V) to the backlight lamp as shown at steps S4, S5. However, the backlight lamp does not instantly output light at a brightness corresponding to the input current (5.5 mA), because of the luminescent characteristics of the backlight lamp, but the brightness of the backlight lamp increases slowly and is outputted as a stable state only after the power supplied to the backlight reaches to 5.5 mA after a certain time passage.
Herein, the luminescent characteristics of the backlight lamp can be different according to its thickness, length, kinds of enclosed gas of the lamp, the luminescent characteristics of the LCD lamp used for a general note PC are stabilized only after about 30 minutes have passed after the first lighting. In addition, the luminescent characteristics are sensitive to the temperature, and in a low temperature condition the rate of increase of the brightness is slower.
Accordingly, a LCD manufacturer defines a measurement reference time point of the brightness as “30 minutes after first lighting”. According to the luminescent characteristics of the backlight lamp, the backlight lamp gradually radiates from the early lighting time point and only radiates fully after a certain time. In more detail, the inverter transmits an output corresponding to a tenth level (herein, 5.5 mA) to the backlight lamp and consumes power corresponding to the output level(herein, 5 Watts); however the backlight lamp shows a full brightness only after 30 minutes due to the characteristics of the backlight lamp.
Accordingly, as depicted in FIG. 2, the inverter continuously consumes 5 Watts from the early lighting in order to output the 5.5 mA driving current, but the brightness of the backlight lamp is actually less than 4 Watts from the early lighting to 10 minutes, 4.5 Watts after 20 minutes from the early lighting, and 5 Watts after 30 minutes from the early lighting.
In more detail, in the method for controlling the backlight lamp in accordance with the prior art, in supply of power to a backlight lamp through an inverter, lots of power is consumed unnecessarily in an early lighting by not considering the luminescent characteristics of the backlight lamp.